Evaluation Of The Effectiveness Of Global Protected Area Vegetation Conservation Based On LAI/NPP

P Protected areas are important sites for the conservation of species and vegetation by improving and enhancing the habitat conditions and viability of vegetation through in situ conservation,thereby slowing the loss of plant diversity.Studying the effectiveness of vegetation conservation in protected areas globally is important for the differentiated conservation and plant diversity preservation in protected areas.However,existing studies have mostly assessed the overall effectiveness of protected areas in stopping deforestation from the perspective of the whole protected area system,and less often have conducted the effectiveness assessment of protected areas from the perspective of vegetation change,which is insufficient guidance for the regulation of nature reserves and the adjustment of conservation priorities.A total of 2762 protected areas in three categories of strict nature reserves,wilderness areas,and national parks were used as the subjects of the study,and global LAI and NPP data were obtained to assess the effectiveness of protected areas in protecting vegetation globally using Mann-Kendall trend test,Theil-Sen slope estimation,and statistical analysis.The results of the study showed that.(1)From 2001 to 2018,the global LAI/NPP values all showed a fluctuating increasing trend.Among them,LAI generally increased at an annual growth rate of 0.0007m~2m^-2(R~2=0.087,P=0.234),with an abrupt change in 2016.n PP generally increased at an annual growth rate of0.050g Cm^-2yr^-1(R~2=0.083,P=0.247),with an abrupt change in 2015.Overall,the area improved by LAI(46.80%)was greater than the area degraded(41.15%),with the former about 6 percentage points more than the latter.The area improved by vegetation NPP(48.79%)was comparable to the area degraded(48.61%).In general,LAI increased in the arid climate zone and temperate cold-temperate zone and decreased in the tropical,subtropical and polar zones;NPP increased in the arid climate zone and temperate cold-temperate zone and decreased in the tropical and subtropical zones,with the least significant changes in the polar zones.(2)The LAI/NPP of global protected areas are all higher than the global average value,and the change of LAI is not obvious,but the NPP has a clear decreasing trend.The mean value of LAI of global protected areas is 2.19m~2m^-2,which is 0.89m~2m^-2 more than the mean value of global LAI of 1.30m~2m^-2 in the same period,and 1.68 times more than the mean value of global LAI.The mean NPP of the global protected areas was 188.29g Cm^-2yr^-1,61.16g Cm^-2yr^-1 more than the global NPP mean of 127.13g Cm^-2yr^-1 over the same period,and 1.48 times the global NPP mean,decreasing significantly at a rate of 0.152g Cm^-2yr^-1per year(R~2=0.353,P=0.009).(3)Global protected areas still had good conservation validity for vegetation LAI/NPP,but this validity showed a significant decreasing trend.The mean value of the conservation effectiveness of global protected areas on vegetation LAI was 0.89m~2m^-2,and it showed a significant decreasing trend at the rate of 0.002m~2m^-2 per year(R~2=0.519,P=0.001).The mean value of the conservation effectiveness of global protected areas on global vegetation NPP was 61.16 g Cm^-2yr^-1 and showed a significant decreasing trend at a rate of 0.202 g Cm^-2yr^-1 per year(R~2=0.7,P<0.01).(4)There were significant differences in the conservation efficacy of LAI/NPP among climate zone reserves.Tropical reserves had insignificant protective validity for LAI,tropical reserves had ineffective protective validity for NPP,and polar zone reserves had the fastest decreasing protective validity for LAI/NPP.Arid climate zone reserves had better protection effectiveness for NPP,and temperate cold climate zone reserves had the lowest and fastest decreasing protection effectiveness for NPP.The effectiveness of LAI protection in each climate zone reserve was in descending order:subtropical(1.92m~2m^-2)>polar(0.82m~2m^-2)>arid(0.72m~2m^-2)>temperate cold(0.47m~2m^-2)>tropical(-0.14m~2m^-2),and the polar zone decreased at a rate of0.005(m~2m^-2)per year,with the most significant decreasing trend.The decreasing trend is the most obvious.The effectiveness of NPP protection in each climate zone was from arid climate zone(55.03g Cm^-2yr^-1)>polar zone(51.44 g Cm^-2yr^-1)>subtropical zone(40.45g Cm^-2yr^-1)>tropical zone(9.75 g Cm^-2yr^-1)>temperate cold climate zone(9.74g Cm^-2yr^-1),and the rate of decrease was 0.294g Cm^-2yr^-1 per year in temperate cold climate zone.The decreasing trend was most obvious in the temperate cold temperate zone with a rate of 0.294g Cm^-2yr^-1 per year.(5)The decrease of LAI conservation effectiveness in temperate cold-temperate and subtropical protected areas was the main reason for the decrease of LAI conservation effectiveness of vegetation in protected areas globally,and the decrease of NPP conservation effectiveness in temperate cold-temperate and polar zone protected areas was the main reason for the decrease of NPP conservation effectiveness in protected areas globally.The changes of LAI/NPP conservation effectiveness of vegetation in different climate zones are correlated with the changes of temperature and precipitation,specifically:except for the temperate cold temperate zone where LAI/NPP conservation effectiveness is significantly affected by temperature,the correlation between LAI/NPP conservation effectiveness of vegetation and temperature and precipitation in all other climate zones is not significant.